Did the test solution react with the supernatant from the test tube that had the largest amount of precipitate? what can you infer about the molar ratio of this reaction?

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The test solution reacted with the supernatant from the test tube. In trial number 3 there was the largest amount of precipitate.

An amount of 0.019 g of precipitate was found. In trial 3, 3 mL CuSO₄ and 3 mL Na₂S was taken. Thus they were at a 1: 1 ratio.

From the fact that the most amount of precipitate was formed when the two reactants were at 1:1 ratio implies that at that ratio, all of the reactants reacted.

Thus the mole ratio of the reaction is 1 : 1.